An optical transistor is an optical device for use in optical circuits that has the characteristics analogous to those of an electrical transistor. For example, an optical transistor may have three terminals or ports analogous to the three terminals of a common BJT or FET transistor. In general, a transistor-type device has the general characteristic of allowing a relatively weak input signal to control a stronger output signal. In an FET, a gate signal with very little current may be used to switch much larger currents.
The ability to allow a weak signal to switch a strong signal is known as the supply-gate ratio (“SGR”). A transistor having a good SGR (for example, a FET or BJT) can be used as a repeater in a transmission line, for example. Another important feature of a transistor is its on/off ratio. The on/off ratio measures the difference in output (e.g. drain-source) current from the on state (conducting) to the off state (non-conducting). This is sometimes known as the blocking characteristic.
In general, an ideal optical transistor would have a good optical SGR and on/off ratio. Such an optical transistor would be useful in all-optical information processing. While optical transistors have been realized, they have only been realized in non-silicon chip environments. Such devices are difficult to incorporate into integrated optical circuits.
There is a need, therefore, for an optical device that operates in the manner of an electrical transistor, but can be implemented in a silicon chip environment that is suitable for integration with other components.